<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        html{
            height: 100%;
        }

        body{
            height: 100%;
        }

        .main{
            height: 100%;
            display: flex;
            justify-content: center;
            align-items: center;
        }
    </style>
</head>
<body>
<div class="main">
    <div class="container content">
        <h1>欢迎</h1>
    </div>
</div>
</body>
</html>